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consolidate nameidata_..._drop_rcu()

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Merge these into a single function (unlazy_walk(nd, dentry)),
kill ..._maybe variants

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-03-25 10:32:48 -04:00
parent 1be6a1f89f
commit 19660af736
1 changed files with 46 additions and 105 deletions
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151
fs/namei.c
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@ -391,79 +391,28 @@ void path_put(struct path *path)
}
EXPORT_SYMBOL(path_put);
/**
* nameidata_drop_rcu - drop this nameidata out of rcu-walk
* @nd: nameidata pathwalk data to drop
* Returns: 0 on success, -ECHILD on failure
*
/*
* Path walking has 2 modes, rcu-walk and ref-walk (see
* Documentation/filesystems/path-lookup.txt). __drop_rcu* functions attempt
* to drop out of rcu-walk mode and take normal reference counts on dentries
* and vfsmounts to transition to rcu-walk mode. __drop_rcu* functions take
* refcounts at the last known good point before rcu-walk got stuck, so
* ref-walk may continue from there. If this is not successful (eg. a seqcount
* has changed), then failure is returned and path walk restarts from the
* beginning in ref-walk mode.
*
* nameidata_drop_rcu attempts to drop the current nd->path and nd->root into
* ref-walk. Must be called from rcu-walk context.
* Documentation/filesystems/path-lookup.txt). In situations when we can't
* continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
* normal reference counts on dentries and vfsmounts to transition to rcu-walk
* mode. Refcounts are grabbed at the last known good point before rcu-walk
* got stuck, so ref-walk may continue from there. If this is not successful
* (eg. a seqcount has changed), then failure is returned and it's up to caller
* to restart the path walk from the beginning in ref-walk mode.
*/
static int nameidata_drop_rcu(struct nameidata *nd)
{
struct fs_struct *fs = current->fs;
struct dentry *dentry = nd->path.dentry;
int want_root = 0;
BUG_ON(!(nd->flags & LOOKUP_RCU));
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
want_root = 1;
spin_lock(&fs->lock);
if (nd->root.mnt != fs->root.mnt ||
nd->root.dentry != fs->root.dentry)
goto err_root;
}
spin_lock(&dentry->d_lock);
if (!__d_rcu_to_refcount(dentry, nd->seq))
goto err;
BUG_ON(nd->inode != dentry->d_inode);
spin_unlock(&dentry->d_lock);
if (want_root) {
path_get(&nd->root);
spin_unlock(&fs->lock);
}
mntget(nd->path.mnt);
rcu_read_unlock();
br_read_unlock(vfsmount_lock);
nd->flags &= ~LOOKUP_RCU;
return 0;
err:
spin_unlock(&dentry->d_lock);
err_root:
if (want_root)
spin_unlock(&fs->lock);
return -ECHILD;
}
/* Try to drop out of rcu-walk mode if we were in it, otherwise do nothing. */
static inline int nameidata_drop_rcu_maybe(struct nameidata *nd)
{
if (nd->flags & LOOKUP_RCU)
return nameidata_drop_rcu(nd);
return 0;
}
/**
* nameidata_dentry_drop_rcu - drop nameidata and dentry out of rcu-walk
* @nd: nameidata pathwalk data to drop
* @dentry: dentry to drop
* unlazy_walk - try to switch to ref-walk mode.
* @nd: nameidata pathwalk data
* @dentry: child of nd->path.dentry or NULL
* Returns: 0 on success, -ECHILD on failure
*
* nameidata_dentry_drop_rcu attempts to drop the current nd->path and nd->root,
* and dentry into ref-walk. @dentry must be a path found by a do_lookup call on
* @nd. Must be called from rcu-walk context.
* unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
* for ref-walk mode. @dentry must be a path found by a do_lookup call on
* @nd or NULL. Must be called from rcu-walk context.
*/
static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry)
static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
{
struct fs_struct *fs = current->fs;
struct dentry *parent = nd->path.dentry;
@ -478,18 +427,25 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
goto err_root;
}
spin_lock(&parent->d_lock);
spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
if (!__d_rcu_to_refcount(dentry, nd->seq))
goto err;
/*
* If the sequence check on the child dentry passed, then the child has
* not been removed from its parent. This means the parent dentry must
* be valid and able to take a reference at this point.
*/
BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
BUG_ON(!parent->d_count);
parent->d_count++;
spin_unlock(&dentry->d_lock);
if (!dentry) {
if (!__d_rcu_to_refcount(parent, nd->seq))
goto err_parent;
BUG_ON(nd->inode != parent->d_inode);
} else {
spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
if (!__d_rcu_to_refcount(dentry, nd->seq))
goto err_child;
/*
* If the sequence check on the child dentry passed, then
* the child has not been removed from its parent. This
* means the parent dentry must be valid and able to take
* a reference at this point.
*/
BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
BUG_ON(!parent->d_count);
parent->d_count++;
spin_unlock(&dentry->d_lock);
}
spin_unlock(&parent->d_lock);
if (want_root) {
path_get(&nd->root);
@ -501,8 +457,10 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
br_read_unlock(vfsmount_lock);
nd->flags &= ~LOOKUP_RCU;
return 0;
err:
err_child:
spin_unlock(&dentry->d_lock);
err_parent:
spin_unlock(&parent->d_lock);
err_root:
if (want_root)
@ -510,22 +468,6 @@ err_root:
return -ECHILD;
}
/* Try to drop out of rcu-walk mode if we were in it, otherwise do nothing. */
static inline int nameidata_dentry_drop_rcu_maybe(struct nameidata *nd, struct dentry *dentry)
{
if (nd->flags & LOOKUP_RCU) {
if (unlikely(nameidata_dentry_drop_rcu(nd, dentry))) {
nd->flags &= ~LOOKUP_RCU;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
br_read_unlock(vfsmount_lock);
return -ECHILD;
}
}
return 0;
}
/**
* nameidata_drop_rcu_last - drop nameidata ending path walk out of rcu-walk
* @nd: nameidata pathwalk data to drop
@ -1241,13 +1183,8 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
if (likely(__follow_mount_rcu(nd, path, inode, false)))
return 0;
unlazy:
if (dentry) {
if (nameidata_dentry_drop_rcu(nd, dentry))
return -ECHILD;
} else {
if (nameidata_drop_rcu(nd))
return -ECHILD;
}
if (unlazy_walk(nd, dentry))
return -ECHILD;
} else {
dentry = __d_lookup(parent, name);
}
@ -1303,7 +1240,7 @@ static inline int may_lookup(struct nameidata *nd)
int err = exec_permission(nd->inode, IPERM_FLAG_RCU);
if (err != -ECHILD)
return err;
if (nameidata_drop_rcu(nd))
if (unlazy_walk(nd, NULL))
return -ECHILD;
}
return exec_permission(nd->inode, 0);
@ -1357,8 +1294,12 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
return -ENOENT;
}
if (unlikely(inode->i_op->follow_link) && follow) {
if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))
return -ECHILD;
if (nd->flags & LOOKUP_RCU) {
if (unlikely(unlazy_walk(nd, path->dentry))) {
terminate_walk(nd);
return -ECHILD;
}
}
BUG_ON(inode != path->dentry->d_inode);
return 1;
}